Merge pull request #38 from maxkudla/update-random-engine

update random engine logic, add test

contracts/pandora/lottery/RandomEngine.sol

@@ -3,16 +3,24 @@ pragma solidity ^0.4.23;
 import "./ILotteryEngine.sol";
 
 contract RandomEngine is ILotteryEngine {
+    bytes32 baseHash;
+    uint256 lastBlockNumber;
 
     constructor()
     public {
+        lastBlockNumber = block.number;
     }
 
     // Current implementation able to return one unique value per block
-    //todo add request count dependency
     function getRandom(uint256 _max)
     public
     returns (uint256 o_result) {
-        o_result = (uint(blockhash(block.number)) + uint(blockhash(block.number - 10))) % _max;
+        if (block.number > lastBlockNumber) {
+            lastBlockNumber = block.number;
+            baseHash = keccak256((uint256(blockhash(block.number)) + uint256(blockhash(block.number - 10))));
+        } else {
+            baseHash = keccak256(baseHash);
+        }
+        o_result = uint256(baseHash) % _max;
     }
 }

test/test_pandora_lottery_random_engine.js

@@ -0,0 +1,19 @@
+const RandomEngine = artifacts.require('RandomEngine');
+
+contract('RandomEngine', accounts => {
+
+    let max = 9999;
+    let engine;
+
+    before('setup test random engine', async () => {
+        engine = await RandomEngine.new();
+    });
+
+    it('should return different numbers each call', async () => {
+        const [r1, r2] =  await Promise.all([
+            engine.getRandom.call(max),
+            engine.getRandom.call(max),
+        ]);
+        assert.isOk(r1 !== r2, 'random is the same as previous');
+    });
+});